1. Field of the Invention
The invention relates to an orthodontic appliance for use in orthodontic therapy. The orthodontic appliance includes brackets and an arch. The invention also relates to a bracket for use in an orthodontic appliance. The invention also relates to an arch for use in an orthodontic appliance.
2. Description of the Related Art
Orthodontic therapy has a long tradition, beginning with an arch designed by Pierre Fauchard in 1728.
In 1887, Edward H. Angle designed the then revolutionary "E-arch" which enabled tooth crowns to be correctly tilted. Angle realized the deficiencies in this technique and subsequently developed the "Pin and Tube" system which enabled even the roots of teeth to be correctly induced. This was the first method which required bands with special securing or anchoring members.
After that, Angle developed "The Ribbon Arch," which required brackets. These brackets were small metal plates, with dimensions of 0.036 in. (1.4 mm) and 0.022 in. (0.87 mm). Each of the plates was individually cemented to a tooth. These brackets were used for a long time. They were not modified until 1956 by Begg, the "Light Wire" technique.
Angle introduced the "Edgewise technique" in 1925 and published his findings in The Dental Cosmos. Dec. 1928, "The Latest and Best in Orthodontic Mechanism." Angle emphasized that no other orthodontic treatment had ever been tested more thoroughly before being publicly introduced. Angle also emphasized the significance of balance in the treatment of a malocclusion.
The Edgewise technique displaces teeth in three planes with a single rectangular or quadratic arch. The edgewise arch is formed of a rectangular wire with dimensions of 0.022 in. (0.87 mm) and 0.028 in. (1.1 mm) or 0.025 in. (0.98 mm). The arch is incorporated into brackets or soldered onto ribbon cemented to the patient's teeth. A gold-platina alloy was used for the ribbon, brackets, and arches before stainless steel came into use. Loops and spurs are soldered onto the ribbon and form attachments when soldering the arch. An ideal arch is constructed at the start of treatment. If irregularities are too great, the arch is gradually modified. For serious anomalies, a round arch, with a diameter of 0.022 in. (0.87 mm), is used, or an edgewise arch with dimensions of 0.022 in. (0.87 mm).
Angle's pupils, Brodie and Strang, were responsible for the next phase in the development of the Edgewise technique. They improved the ribbons and brackets, introduced new materials, used rounder arches, and made other changes.
In 1930, Charles Tweed drew attention both to the necessity of extraction and the significance of the anchoring mechanism. Tweed also determined that an orthodontic apparatus should be able to create constant maximal resistance in the anchoring region and minimal resistance in the region in which displacement was desired.
In 1953, Steiner proposed the use of 0.018 in. (0.71 mm) slot brackets and arches of stainless steel, and found that the treatment period was reduced. Steel replaced gold during the years following and many orthodontists started using such brackets.
Efforts have been made in recent years to improve upon the prior art by making arches of thinner material, and by making other minor changes.
However, such designs have many serious drawbacks. For example, it has been established that undesirable metal ions are dissolved out of stainless materials by the constant influence of saliva.
Furthermore, the use of stainless material for the brackets produces an extremely unattractive appearance. However, repeated attempts to improve aesthetics by manufacturing brackets of bone-colored plastic materials have been unsuccessful. Such plastic materials have been too brittle and the brackets formed of such material have not been strong enough, particularly if a relatively strong metal wire is used in the arch.
To solve this problem, attempts have been made (U.S. Pat. No. 4,302,532) to reinforce the archwire slots in such plastic brackets with special coatings or liners of harder material, such as metal, to reduce wear between the steel arch and the archwire slot. This has improved the wear resistance of orthodontic appliances. However, the prior art plastic materials are still too brittle and too affected by the constant influence of saliva. Moreover, the reinforcement described in U.S. Pat. No. 4,302,532 is extremely complicated and becomes detached in practice due to friction between the archwire and the reinforcement. Moreover, such reinforced plastic brackets are expensive to manufacture and are unattractive.
It has also been proposed (U.S. Pat. No. 4,180,912) to improve the appearance of orthodontic appliances by providing conventional steel brackets with an outer casing of plastic. However, this proposal is extremely complicated and the casings are often damaged by the arch. The proposal is nonfunctional in practice.
Ceramic brackets have also been tried. However, such ceramic brackets cause wear while adhered to tooth enamel and cause surface damage when finally removed.
Therefore, stainless steel is still generally used in brackets and arches.
Finally, an orthodontic appliance which is built up on the lingual surfaces of a patient's teeth is disclosed in Sweden Patent No. 85 01 579-0. However, the patient continually encounters the various parts of such an appliance with the tip of the tongue and it is difficult to maintain an acceptable level of hygiene.